This invention relates in general to conveyor systems and, in particular, to a heavy duty conveyor system such as used as an elevator on a carry-type scraper wherein the elevator is used to move material into the scraper bowl.
More specifically, but without restriction to the particular use which is shown and described, this invention relates to a mounting for a conveyor or elevator drive to prevent elevator sprocket shaft load-initiated deformation or deflection, and torsional vibration, from causing undue stress on the drive mechanism and particularly on the gear reduction output shaft and bearings contained therein.
Proper alignment between the drive mechanism and an elevator sprocket shaft driven therefrom is particularly important in heavy duty conveyor systems. Rigid mounting of the gear housing, which contains drive reduction gears and an output shaft for coupling to the sprocket shaft, has been found to be undesirable. The sprocket shaft, being relatively long, must be supported for rotation at both laterally positioned ends and be close coupled at one end to the geared drive shaft. Such a shaft and gear reduction housing combination is frequently subjected to misalignment stresses caused by both manufacturing variations when the parts are produced and operational induced loading. Further misalignment is caused by bending loads imposed on the elevator frame and the sprocket shaft. These induced stresses occur along with torsional vibrations which occur when the elevator moving material into the scraper bowl strikes rocks or other such material and frequently results in damage to the elevator system.
Scrapers generally include a box-type structure, referred to as a "bowl", open at its forward end with the bottom or floor of the bowl having an adjustable forward cutting edge adapted to cut a predetermined amount from the upper surface of the ground. The bowl is normally open at its forward end so that the material cut by the cutting edge as it moves through the ground will pass into the bowl. However, as the material is cut it accumulates adjacent to the cutting edge and does not spread uniformly throughout the scraper bowl. Therefore, a conveyor or flight-type elevator must be carried within the bowl and positioned above and to the rear of the cutting edge to receive the material as it is passed into the forward portion of the bowl to move it both rearwardly and upwardly for more complete filling.
These elevators generally comprise a pair of rigidly joined side frame members extending the full length of the elevator and carrying idler wheels at the lower forward end and sprockets at the upper rear end which engage endless link-type chains of a flight-type elevator. Such elevators are normally provided with a mounting frame structure carried on the scraper bowl which permits floating action of the elevator over dirt or material entering the bowl to prevent damage to the elevator or cutting edge when a large stone or other object is hit by the scraper. However, while such structure prevents damage by permitting the elevator to float when large stones or hard material is hit repeatedly, hitting these stones causes torsional vibrations in the drive system frequently damaging the elevator flights because of the rotating inertia of the drive mechanism. Also sprocket shaft deflection, caused by the same action that causes torsional vibration, as well as the occasional trapping of rocks or stones between the sprocket shaft and one or more of the elevator flights, causes deflection of the shaft and misalignment resulting in severe loading of bearings located between the driving mechanism and the driven sprocket shaft.
Other prior art elevator drive mechanisms are resiliently supported on the elevator frame which, to some extent, overcomes some of the adverse effects of the aforementioned sprocket shaft deflection. For example, U.S. Pat. No. 3,543,915 discloses a pivot connection mounting of the drive mechanism on the elevator frame and U.S. Pat. No. 3,046,859 discloses a similar mounting structure.
Another attempt to provide a solution to these problems is disclosed in U.S. Pat. No. 3,738,031 wherein a drive mechanism is pivoted for rocking movement about the elevator drive shaft, and includes a spring positioned between the drive mechanism housing and a frame to permit limited rocking in response to reaction torque which is incurred when shock loads are encountered by the elevator.
While the prior art has provided improved structures to solve the problems of misalignment and torsional vibration, the present invention solves the problem to a greater extent by a simple rugged structure. While this invention is believed to have general applications to all types of conveyor systems, for convenience of illustration, a preferred embodiment will be described with reference to its use in the elevator of a scraper.